Thermostat with overlapped bimetal control strips therein

ABSTRACT

A thermostat, thermal protector, or the like is provided including a shunt strip extending into the casing in cantilever form and where a pair of opposed contacts are usually carried by the free end of the shunt arm and the inside wall of the case in opposed relation. A bimetal strip is secured as a cantilever and its free end overlaps with the free end of a second bimetal strip secured to the shunt arm adjacent the free end thereof and extending towards the secured end of the first bimetal strip to overlap the first bimetal strip and normally have the free ends thereof in pressure contact.

United States Patent 3,012,119 12/1961 Barrett [72] Inventor Alton R.Wells 337/1 12 X 4573 West Trade Winds Ave., Lauderdale- 2,004,963 6/1935 Scharf 73/3635 X by-the-Sea, Fla. 33308 1,916,671 7/1933 Hanser etal 337/370 X [2]] 1 1970 Primary Examiner-Bernard A. Gilheany [22] e S1971 Assistant Examiner Dewitt M. Morgan [451 Attarney0ldham & Oldham[54] THERMOSTAT WITH OVERLAPPED BIMETAL CONTROL STRIPS Tl-lERElN 8Claims, 2 Drawing Figs.

[52] U.S. Cl 337/95,

337/112 ABSTRACT: A thermostat, thermal protector, or the like is [51]Int. Cl ..H0lh37/52, provided including a shunt strip extending i hCasing in H01h61/013H01h61/O6 cantilever form and where a pair ofopposed contacts are [50] Field 01' Search 337/38, 39, usually carriedby the f end f the shunt arm and the inside 95, 96, wall of the caseinopposed relation. A bimetal strip is secured 380; 73/3635 as acantilever and its free end overlaps with the free end of a 56 R I dsecond bimetal strip secured to the shunt arm adjacent the 1 e erencesfree end thereof and extending towards the secured end of the UNITEDSTATES PATENTS first bimetal strip to overlap the first bimetal stripand nor- 3,21 1,863 10/1965 Levinn 337/107 mally have the free endsthereofin pressure contact.

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INVENTOR.

ALTON R. WELLS www ATTORNEYS.

THERMOSTAT WITH OVERLAPPED BIMETAL CONTROL STRIPS THEREIN l-leretoforethere have been many different types of thermostats, thermal protectorsand the like provided. However, in all of such articles, there always isa demand to have a low price, relatively uncomplicated control providedwhich will function under varying types of circuit conditions.Particularly, where relatively heavy currents, such as up to and over 60amps are present in the control circuit, most cantilever types ofthermostats available heretofore have not been completely satisfactoryfor use in these relatively high-amperage power circuits for controlaction therein.

' The general object of the present invention is to provide an improvedthermostat or similar article wherein a shunt strip is provided as acurrent carrying element extending into the thermostat casing as acantilever and wherein a pair of overlapped opposed bimetal strips areprovided in the casing with only one of such bimetal strips beingsecured to the shunt arm adjacent the free end thereof.

Another object of the invention is to use a pair of overlapping butindependent bimetal control strips in a thermostat or similar articleand wherein such bimetal strips are heated by conduction from thecontact and the shunt arm and by radiation from the shunt arm, and/or byheat flow through the insulating means positioning the shunt arm andbimetal strip in the thermostat.

Another object of the invention is to provide an improved thermalcontrol adapted to carry relatively high amperage and which will providea definite "one time" for a circuit with a given amperage currentflowing in the circuit.

The foregoing and other objects and advantages of the present inventionwill be made more apparent as the specification proceeds.

Reference is made to the accompanying drawings, which show:

FIG. 1 is a vertical section of a thermostat embodying the principles ofthe invention, as oneillustration of an article of the invention, withthe contacts closed; and

FIG. 2 is a similar vertical section with the contacts open of amodified embodiment of the invention,

Havingparticular reference to the details of the structure shown in thedrawing, a thermostat is indicated. This thermostat or equivalentarticle includes a substantially conventional metal or other type ofcase or casing 11 which normally has one initially open end 12 and aclosed end 13 therein. A shunt arm or-strip 14 is secured in the case 11and extends thereinto as a cantilever, being positioned at the initiallyopen end 12 of the case by being compressively engaged with conventionalmeans such as an insulation sleeve 15 that can be made from aresin-impregnated fiberglass, or other equivalent material. A pair ofopposed contacts 16 and 17 are secured, respectively, to the free end ofthe shunt arm 14 and to the inner wall of the case 11 in opposedrelation, which contacts are of conventional design and construction.

As a feature of the present invention, the insulation means or sleeve 15is also used to position the first bimetal strip 18 in insulatedrelation to both the case 11 and the shunt arm 14 so that the bimetalstrip 18 extends into the case normally in substantially parallelrelation to the shunt arm 14. A further feature of the invention residesin a second bimetal strip 19 one end of which is secured in good thermalconductive relation to the shunt arm 14 adjacent or at the free endthereof, as by being welded thereto. Such second bimetal strip 19 has anoffset or inclined section 20 formed therein whereby the second bimetalstrip 19 is positioned for the major part of its length in offsetrelation to the shunt arm 14 but usually extending substantiallyparallel thereto. The free end of the second bimetal strip 19 extendstowards the initially open end of the case 11 and overlaps the free endof the first bimetal strip 18. Preferably, both of these bimetal strips18 and 19 are of such a construction that they both curve upwardly fromthe secured portions thereof when heated and the free ends of thesestrips may be in contact or be spaced from each other depending upon thethen specific phase of the operating cycle. The arm 18 engages the arm19 to move it and contact 16 for circuit opening action.

It will be seen that the current flow in the thermostat 10 normally isthrough the casing 11 and through the shunt arm 14 and any suitableterminal means are provided for connecting power leads thereto. Theinitially open end of the case 11 can be processed in any suitablemanner to compress such case end and enclose and seal the bimetal strip18 and shunt arm 14 in the thermostat in operative positions.

It will be seen that the lengths of the bimetal strips 18 and 19 can bevaried and the compositions of such bimetal strips can be varied wherebythe curvature rates thereof and action when heated can be controlled andchanged. Naturally it is the curvature action of the bimetal strips 18and 19 in association with each other that serve to force the shunt arm14 upwardly of the case 11 to open the contacts 16 and 17 and thecircuit controlled thereby. The shunt arm 14 can be made either from aheat resistant material, as one which heats up rapidly under currentcarrying conditions (lnconel 320-7 for example), or the shunt arm can bemade from a good electrical conductor with a minimum of heat beinggenerated therein; and the heat created within the case 11 can be variedand thus the opening and closing characteristics of the thermostat 10can be varied widely within desired limits. The shunt arm normally isnot made from a bimetal material.

By the construction of the invention, the bimetal strips 18 and 19normally relax or tend to straighten slowly after the contacts 16 and 17have been opened and then the bimetals permit the shunt arm 14 to movedown slowly to bring the contacts 16 and 17 into engagement again.Arcing between the contacts is avoided by a positive continued-closingaction of the moving contact 16, and no tendency to initiate an openingforce is set up in the bimetal strips at the instant when current flowis resumed through the'thermostat 10. That is the strips 18 and 19 arestill cooling and are not immediately heated by any initial current flowas such strips are nonconductive in the thermostat circuit. lf thearcing should occur under high voltages, the action of the bimetals issuch as to extinguish the are, as by increasing the closing pressure.Hence, the contacts do not tend to chatter or arc on either the openingor the closing of circuit conditions. Of course, the shunt arm, orconductor 14 is so positioned in the thermostat as to have a normalposition to engage contact 16 with contact 17.

By increasing the length of the bimetal strip 19 in relation to thelength of the bimetal strip 18, the hot one" and cycle times areincreased and vice verse. The bimetals l8 and 19 need only sufficientoverlap to insure contact therebetween for circuit opening action. Thebimetal arm 18 for example may be about iii to 3 times as long as thebimetal arm 19, and

usually is about twice as long as such arm 19 to provide the majorcontact opening force.

The thermal protector 10 usually is used where the casing 13 is subjectto high environmental heating which casing transmits heat to the strips18 and 19 by radiation. in use, the bimetal strip 18 is heated slowlyprimarily by external heat flow to the casing 13 for radiating heat tothe strip 18. The strip 19 is heated more rapidly by being in additionalheat conducting contact with the current carrying shunt arm 14.Therefore the action to create an opening force on the arm 14 is delayedby the bimetal arms in combination until the upwardly movable bimetalarm 18 is extensively heated and moves substantially to overtake andcontrol the upward moving arm 19 and thus the shunt arm 14 securedthereto. As the bimetal arm 19 cools, it-straightens and exerts pressureon the lower arm 18 and reaction pressure on the shunt arm 14 to urge itupwardly and open the contact further. Hence the cooling of the bimetalarm 19 tends to maintain the contacts open and maintain a cooling actionon the environment to which the thermal protector 10 is subjected, Ofcourse the free end of the arm is offset further from the shunt arm 14than the distance that such arm 19 will curve upwardly when heated.Usually it is desirable that no appreciably heat flow occurs between thebimetal strips when in contact and one bimetal strip may have a suitableinsulation means secured thereto at the area that would engage the otherbimetal arm to minimize heat flow therebetween. Or, a small end area ofone bimetal strip can be embossed to protrude towards the other bimetalstrip in the overlapped portions thereof to provide a small nubbin, ordimple 21 for contact with the other bimetal strip. Such dimple 21 isusually a section of a sphere and protrudes from the adjacent flat stripat least 0.004, preferably 0.006 to 0.008 inch. If the thermal protectoris to operate at two different voltages such as about 110 to 120 or 220to 240 volts, then an insulated lead 25 has an end thereof secured,usually welded, to the shunt arm 14 at its free end. The lead 25 extendsthrough and is sealed by the insulation material 15 for connection tothe alternate high-voltage circuit. For high currents, it is notdesirable to have the bimetal strip or strips in the circuits because ofthe sensitivity of bimetals to the rapid current heating action thereof.Likewise the shunt arm 14 would be heated rapidly by its currents underthe elevated voltage and hence action of the thermal protector is sloweddown by use of the lead as shown.

The casing 11 may be conductive or not, as desired, and the contact 17may have a lead extending therefrom to and through the open end of thecasing. Both ends of the casing may be open, if desired and thethermostat may have a second conventional bimetal arm extendingthereinto from the opposite end, as shown, for example, in U.S. Pat. No.2,586,309. Such second arm would carry a contact for engaging thecontact 16 on the shunt arm 14 and would move away from such arm 14 whenheated. The thermal protectors may be calibrated as disclosed in U.S.Pat. Nos. 2,497,397 and 2,586,309. The sealed end or ends of the thermalprotector may be of the construction disclosed in U.S. Pat. No.3,209,107.

Any conventional bimetal strips may be used with the bimetal strip 18normally having, for example, a layer 40 of high-expansion metal such asa nickel-crome-steel alloy, and a layer 41 of a low-expansion metal,such as a nickel-iron alloy therein. W.M. Chace Company of Detroit,Michigan makes a number of known types of bimetals and its No. 2,400 istypical of the bimetal strips in use today. The bimetal strip 19normally is made from the same material as the strip 18 with the samepositioning of the high and low-expansion metals.

FIG. 2 shows a modified thermostat 10a similar to the thermostat 10 butwith an insulation sleeve secured suitably to the free end of a bimetalstrip 180. In this instance, the thermostat is shown with the contactsopen but where cooling of the thermostat has started and a bimetal strip19a has started to curve downwardly.

The thermostats or motor protectors of the invention may have adifferential in temperature of opening and closing action in the range,for example, of 5 to 30 F. in thermal controls designed to open in therange, for example, of 165 to l90 F. The thermostats are described asnormally positioned horizontally in the manner shown in FIG. 1. In thethermostat 10a of FIG. 2, the bimetal strip 18a would curve upwardlywhen the contacts are open and FIG. 2 shows the strip 18a when it hascooled down almost to circuit closing position. Any suitable insulationmeans 30 is positioned intermediate the ends of the strips 18a and 19a.

In view of the foregoing, it is believed that the objects of theinvention have been achieved.

While one complete embodiment of the invention has been disclosedherein, it will be appreciated that modification of this particularembodiment of the invention may be resorted to without departed from thescope of the invention.

What is claimed is:

l. A thermostat, thermal protector or the like comprising a casinghaving at least one open end, a bimetal strip extending into the casingas a cantilever, insulation means securing said strip at the initiallyopen end of said casing and sealing said open end and around saidbimetal strip, a shunt strip secured as a cantilever extending into saidcasing and insulated from both said bimetal strip and said casing at thesecured end of said shunt strip, opposed contact means on said casingand the free end of said shunt strip and said shunt strip and saidcasing being adapted to have power leads secured thereto operativelyconnecting to said contact means, characterized by said bimetal stripbeing below and shorter than said hunt strip,

a second bimetal strip secured at one end to the free end of said shuntstrip and extending towards the initially open 'end of said casing, saidsecond bimetal strip being offset from said shunt strip except for ashort distance adjacent is secured end, said second bimetal strip havinga free end overlying the free end of said first bimetal strip.

2. A thermostat, themial protector or the like as in claim 1 where bothof said bimetal strips move upwardly when heated, and where the cyclerate of the thermostat can be varied by changing the respective lengthsand compositions of said bimetal strips.

3. A thermostat, thermal protector or the like as in claim 1 where saidsecond bimetal strip is shorter than said first bimetal strip.

4. A thermostat, thermal protector or the like as in claim 1 where acurrent conducting lead extends into said casing and is secured to saidshunt strip immediately adjacent to a said contact means.

5. A thermostat, thermal protector or the like comprising a casinghaving at least one end, a bimetal strip extending into the casing as acantilever, insulation means securing said strip at the initially openend of said casing and sealing said open end and around said bimetalstrip, a shunt strip secured as a cantilever extending into said casingand insulated from both said bimetal strip and said casing at thesecured end of said shunt strip, opposed contact means being providedwithin said casing with one of said contact means being operativelysecured to the free end of said shunt strip, and said shunt strip beingadapted to have a power lead secured thereto characterized by saidbimetal strip being spaced from and shorter than said shunt strip butmovable towards said shunt strip when heated,

a second bimetal strip secured at one end to the free end of said shuntstrip and extending towards said initially open end of said casing, saidsecond bimetal strip normally being offset from said shunt strip exceptfor a short distance adjacent is secured end, said second bimetal striphaving a free end positioned intermediate the free end of said bimetalstrip and said shunt strip when considering the positions in a directionperpendicular to the longitudinal axis of said casing 6. A thermostat,thermal protector or the like as in claim 5 comprising a said bimetalstrip being spaced from a shorter than said shunt strip but movabletowards said shunt strip when heated, and

said second bimetal strip which is above said bimetal strip movingtoward said shunt strip when heated,

the action of said bimetals resulting in a closing action of thecontacts at a significantly lower temperature than the temperature atthe opening action of the contacts.

7. A thermostat, thermal protector, or the like as in claim 5 whereinsulation means are operatively positioned intermediate the free endsof said bimetal strips.

8. A thermostat, thermal protector or the like as in claim 5 andincluding a power lead extending into said casing from said open endthereof, said insulation means insulating said power lead from saidshunt strip, and an end of said power lead being secured to said shuntstrip in the area of the free end thereof.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3.609618 Dated September 28. 1971 Inventor(s) Alton R. Wells It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 1, line 29, "one time should read on time Col. 2, line 47, hot oneshould read "hot on" Col. 2, line 48, "vice Verse" should read viceversa Col. 2, line 75 "appreciably" should read appreciable C01. 3, line67, "departed" should read departing Col. 4, line 8, Claim 1 "hunt"should read shunt Col. 4, line 14, Claim 1, "is" should read its Col. 4,line 29, Claim 5, after "one" insert open C01. 4, line 47, Claim 5 "is"should read its C01. 4, Claim 5, line 51, after "casing" insert Col. 4,line 54, Claim 6, "a" should read and Signed and sealed this 28th day ofMarch 1972.

(SEAL) Attest:

EDIJARD M.FLETCHER, JR. ROBERT GOT'ISCHALK Attesting OfficerCommissioner of Patents po'wso uscoMM-oc 60376-P09 U S GOVERNMENYPRINTING OFFICE l9 O-Jii'll

1. A thermostat, thermal protector or the like comprising a casinghaving at least one open end, a bimetal strip extending into the casingas a cantilever, insulation means securing said strip at the initiallyopen end of said casing and sealing said open end and around saidbimetal strip, a shunt strip secured as a cantilever extending into saidcasing and insulated from both said bimetal strip and said casing at thesecured end of said shunt strip, opposed contact means on said casingand the free end of said shunt strip and said shunt strip and saidcasing being adapted to have power leads secured thereto operativelyconnecting to said contact means, characterized by said bimetal stripbeing below and shorter than said shunt strip, a second bimetal stripsecured at one end to the free end of said shunt strip and extendingtowards the initially open end of said casing, said second bimetal stripbeing offset from said shunt strip except for a short distance adjacentits secured end, said second bimetal strip having a free end overlyingthe free end of said first bimetal strip.
 2. A thermostat, thermalprotector or the like as in claim 1 where both of said bimetal stripsmove upwardly when heated, and where the cycle rate of the thermostatcan be varied by changing the respective lengths and compositions ofsaid bimetal strips.
 3. A thermostat, thermal protector or the like asin claim 1 where said second bimetal strip is shorter than said firstbimetal strip.
 4. A thermostat, thermal protector or the like as inclaim 1 where a current conducting lead extends into said casing and issecured to said shunt strip immediately adjacent to a said contactmeans.
 5. A thermostat, thermal protector or the like comprising acasing having at least one open end, a bimetal strip extending into thecasing as a cantilever, insulation means securing said strip at theinitially open end of said casing and sealing said open end and aroundsaid bimetal strip, a shunt strip secured as a cantilever extending intosaid casing and insulated from both said bimetal strip and said casingat the secured end of said shunt strip, opposed contact means beingprovided within said casing with one of said contact means beingoperatively secured to the free end of said shuNt strip, and said shuntstrip being adapted to have a power lead secured thereto characterizedby said bimetal strip being spaced from and shorter than said shuntstrip but movable towards said shunt strip when heated, a second bimetalstrip secured at one end to the free end of said shunt strip andextending towards said initially open end of said casing, said secondbimetal strip normally being offset from said shunt strip except for ashort distance adjacent its secured end, said second bimetal striphaving a free end positioned intermediate the free end of said bimetalstrip and said shunt strip when considering the positions in a directionperpendicular to the longitudinal axis of said casing
 6. A thermostat,thermal protector or the like as in claim 5 comprising a said bimetalstrip being spaced from and shorter than said shunt strip but movabletowards said shunt strip when heated, and said second bimetal stripwhich is above said bimetal strip moving toward said shunt strip whenheated, the action of said bimetals resulting in a closing action of thecontacts at a significantly lower temperature than the temperature atthe opening action of the contacts.
 7. A thermostat, thermal protector,or the like as in claim 5 where insulation means are operativelypositioned intermediate the free ends of said bimetal strips.
 8. Athermostat, thermal protector or the like as in claim 5 and including apower lead extending into said casing from said open end thereof, saidinsulation means insulating said power lead from said shunt strip, andan end of said power lead being secured to said shunt strip in the areaof the free end thereof.